Habitat-related differences in auditory processing of complex tones and vocal signal properties in four songbirds

Vocalizations of the Pekin duck (Anas platyrhynchos domesticus): how stimuli, sex, and social groups affect their vocal repertoire

Pekin ducks are exposed to stressors such as heat stress, enteric pathogens, mycotoxins, and other environmental stressors. We know from wild bird literature that birds communicate through vocalizations. We hypothesized that Pekin ducks would have a diverse repertoire that is affected by the sex, social group, and specific stimuli. We utilized adult Pekin ducks to develop a vocal repertoire. We placed 1 to 4 ducks of varying sexes into a sound chamber with various stimuli used to encourage new vocalizations. Birds were recorded for 20 min with several variations of number and sexes of ducks. Once the ducks were recorded each vocalization that was clipped was named based on a predetermined naming system. We characterized the vocal system of the ducks under each stimulus and social treatment in 4 ways: overall call rates, call diversity, call repertoire, and call spectral properties. In all cases, normality of residuals and homogeneity of variances for GLM and ANOVA models were confirmed using Proc Univariate (SAS v9.4) where a p ≤ 0.05 was considered significant. We found that Pekin ducks produce up to 16 different vocalizations. The treatments had a significant effect on the overall rate of calls given by the ducks (ANOVA: F6,31 = 8.55, p < 0.0001). Ducks produced the most calls by far when someone was sitting in the chamber with them (30.04 ± 4.45 calls/min). For call diversity, we found that there was a significant main effect of hen number (F218 = 12.21, p = 0.0004) but no main effect of drake number (F3,18 = 3.04, p = 0.0555). Cluster analyses indicated that certain types of calls were given under specific conditions. There were generally 6 major clusters of vocal repertoires (R-square = 0.899, Cubic Clustering Criterion = 9.30). Our results suggest that Pekin ducks are affected by the types of stimuli and social environment in how much they vocalize and in the properties of the calls they use. In addition, males and females differ somewhat in the repertoire of the calls they use, and in the spectral properties of their calls.

Auditory sensitivity and vocal acoustics in five species of estrildid songbirds

Comparative studies of acoustic communication in clades with diverse signal features provide a powerful framework for testing relationships between perception and behaviour. We measured auditory sensitivity in five species of estrildid songbirds with acoustically distinct songs and tested whether differences aligned with species differences in song frequency content. Species were chosen based on phylogeny and differences in song acoustics. Behavioural audiograms were obtained using operant training and testing. Adult audiograms were compared across species and between sexes within a species. Juvenile and adult audiograms were compared in one species. The audiograms of adults reared by their own species and those reared and tutored by another species were compared in one species. Results showed that audiograms were similar across species and similar to previous reports of songbird auditory sensitivity. Species differed in the highest frequency detected and the frequency of peak sensitivity. While hearing frequency range was not correlated with song frequency bandwidth, the frequency of peak sensitivity was highly corelated with the frequency of peak energy in song. Sensitivity did not differ based on sex, age or tutoring experience. Our findings suggest that adaptations in songbird auditory sensitivity are largely constrained by shared peripheral and central encoding mechanisms, with species-specific perception appearing only at peak sensitivity.

Selecting auditory alerting stimuli for eagles on the basis of auditory evoked potentials

Development of wind energy facilities results in interactions between wildlife and wind turbines. Raptors, including bald and golden eagles, are among the species known to incur mortality from these interactions. Several alerting technologies have been proposed to mitigate this mortality by increasing eagle avoidance of wind energy facilities. However, there has been little attempt to match signals used as alerting stimuli with the sensory capabilities of target species like eagles. One potential approach to tuning signals is to use sensory physiology to determine what stimuli the target eagle species are sensitive to even in the presence of background noise, thereby allowing the development of a maximally stimulating signal. To this end, we measured auditory evoked potentials of bald and golden eagles to determine what types of sounds eagles can process well, especially in noisy conditions. We found that golden eagles are significantly worse than bald eagles at processing rapid frequency changes in sounds, but also that noise effects on hearing in both species are minimal in response to rapidly changing sounds. Our findings therefore suggest that sounds of intermediate complexity may be ideal both for targeting bald and golden eagle hearing and for ensuring high stimulation in noisy field conditions. These results suggest that the sensory physiology of target species is likely an important consideration when selecting auditory alerting sounds and may provide important insight into what sounds have a reasonable probability of success in field applications under variable conditions and background noise.

What is known - and not known - about acoustic communication in an urban soundscape

Urban environments have some of the most highly modified soundscapes on the planet, affecting the way many animals communicate using acoustic signals. Communication involves transmission of information via signals, such as bird song, between a signaler and a receiver. Much work has focused on the effects of urbanization on signalers and their signals, yet very little is known about how noise pollution affects receiver behaviors and sensory systems. Here we synthesize key findings to date regarding avian acoustic communication in the urban environment and delineate key gaps in knowledge for future work. We leverage our own work comparing current and historical songs from urban and rural habitats for a subspecies of white-crowned sparrows (Zonotrichia leucophrys nuttalli). We use this system, along with findings from other systems, to answer three key questions in the field: (1) Is song variation consistent with temporal and spatial variation in anthropogenic noise? (2) How are birds adjusting their song to the urban environment? and (3) How does song 'urbanization' affect signal function? Our synthesis illustrates that the adjustments birds make to their songs in noisy environments can improve signal detection, but potentially at the cost of signal function. Many key gaps in knowledge need to be addressed to complete our understanding of how acoustic communication systems evolve in urban areas, specifically in regard to sexual selection and female preference, as well as how receivers perceive signals in an urban environment.

Field testing an "acoustic lighthouse": Combined acoustic and visual cues provide a multimodal solution that reduces avian collision risk with tall human-made structures

Billions of birds fatally collide with human-made structures each year. These mortalities have consequences for population viability and conservation of endangered species. This source of human-wildlife conflict also places constraints on various industries. Furthermore, with continued increases in urbanization, the incidence of collisions continues to increase. Efforts to reduce collisions have largely focused on making structures more visible to birds through visual stimuli but have shown limited success. We investigated the efficacy of a multimodal combination of acoustic signals with visual cues to reduce avian collisions with tall structures in open airspace. Previous work has demonstrated that a combination of acoustic and visual cues can decrease collision risk of birds in captive flight trials. Extending to field tests, we predicted that novel acoustic signals would combine with the visual cues of tall communication towers to reduce collision risk for birds. We broadcast two audible frequency ranges (4 to 6 and 6 to 8 kHz) in front of tall communication towers at locations in the Atlantic migratory flyway of Virginia during annual migration and observed birds' flight trajectories around the towers. We recorded an overall 12-16% lower rate of general bird activity surrounding towers during sound treatment conditions, compared with control (no broadcast sound) conditions. Furthermore, in 145 tracked "at-risk" flights, birds reduced flight velocity and deflected flight trajectories to a greater extent when exposed to the acoustic stimuli near the towers. In particular, the 4 to 6 kHz stimulus produced the greater effect sizes, with birds altering flight direction earlier in their trajectories and at larger distances from the towers, perhaps indicating that frequency range is more clearly audible to flying birds. This "acoustic lighthouse" concept reduces the risk of collision for birds in the field and could be applied to reduce collision risk associated with many human-made structures, such as wind turbines and tall buildings.